Re: [PATCH 4/4] xen/scsifront: harden driver against malicious backend

[Juergen Gross <jgross@xxxxxxxx>]

On 20.04.22 18:13, Boris Ostrovsky wrote:
> Just a couple of nits.
>
>
> On 4/20/22 5:25 AM, Juergen Gross wrote:
> > -static int scsifront_ring_drain(struct vscsifrnt_info *info)
> > +static int scsifront_ring_drain(struct vscsifrnt_info *info,
> > +                unsigned int *eoiflag)
> >   {
> > -    struct vscsiif_response *ring_rsp;
> > +    struct vscsiif_response ring_rsp;
> >       RING_IDX i, rp;
> >       int more_to_do = 0;
> > -    rp = info->ring.sring->rsp_prod;
> > -    rmb();    /* ordering required respective to dom0 */
> > +    rp = READ_ONCE(info->ring.sring->rsp_prod);
> > +    virt_rmb();    /* ordering required respective to backend */
> > +    if (RING_RESPONSE_PROD_OVERFLOW(&info->ring, rp)) {
> > +        scsifront_set_error(info, "illegal number of responses");
>
> In net and block drivers we report number of such responses. (But not in usb)
I'm not sure the specific value is of any interest.

> > +        return 0;
> > +    }
> >       for (i = info->ring.rsp_cons; i != rp; i++) {
> > -        ring_rsp = RING_GET_RESPONSE(&info->ring, i);
> > -        scsifront_do_response(info, ring_rsp);
> > +        RING_COPY_RESPONSE(&info->ring, i, &ring_rsp);
> > +        scsifront_do_response(info, &ring_rsp);
> > +        if (info->host_active == STATE_ERROR)
> > +            return 0;
> > +        *eoiflag = 0;
>
> *eoiflags &= ~XEN_EOI_FLAG_SPURIOUS; ?
Yes, probably better.

> We also use eoi_flags name in other instances in this file.
I'll unify the name.


Juergen

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